Graphene-containing coating film, and method for preparing the same

Cross-reference to related application

This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0119555 filed in the Korean Intellectual Property Office on Aug. 25, 2015, the entire contents of which are incorporated herein by reference.

Technical field

The present invention relates to a graphene-containing coating film and a method of preparing the same.

Background of the invention

Graphene oxide (or graphite oxide, hereinafter GO) is a sheet-shaped carbon material prepared by acid treating graphite, and has a large amount of a hydrophilic functional group such as a carboxyl group (—COOH), a hydroxyl group (—OH), and the like on the surface. The surface oxidizing groups produced through an acid treatment process spontanesouly produce hydrogen-bonds with H.sub.2O molecules, and thus the GO can be prepared in a form of a hydration or in a water-containing slurry state. In general, a solid concentration of the slurry is of about 2 to 8 wt % unless otherwise specifically treated.

When the GO is appropriately included in a film or a structure, strength thereof may be improved and suitable thermal conductivity may be provided, but treatment of the contained moisture may hinder properties.

In general, GO may be prepared in a form of graphene through a chemical reduction method (a hydrazine treatment and the like) and a thermal reduction method. Herein, reduced graphene is particularly referred to as reduced graphene oxide (RGO).

It is evidenced that a part of the oxidizing groups on the RGO surface is not sufficiently removed. Generally, oxygen content of the surface oxidizing groups is less than or equal to about 5 wt % relative to a carbon backbone, and thus graphene (RGO) of the present invention has an oxygen content of less than or equal to about 5 wt % because of the surface oxidizing groups relative to a carbon backbone.

A heterogeneous mixture of GO, and RGO and a conventional material has recently evoked active interest, and this may improve synergic effects between materials exceeding a limit of the conventional material. The heterogeneous mixture may be used in a high strength composite material and a fuel cell. In certain examples, a graphene-nanowire (semiconductor) hybrid structure where light energy is absorbed in a graphene conductive part and electron-hole pairs are generated (KR 10-2012-0092431 A), a hybrid composite manufacturing method including graphene sheet/carbon nanotube/a polymer nanoparticle (KR 10-2012-0053399 A), a method of manufacturing a positive electrode graphene material for a lithium rechargeable battery that is a hybrid material formed by adding an Fe precursor and a PO.sub.4 precursor (KR 10-2012-0035659 A), a method of manufacturing a graphene composite calcinated body having an excellent charge and discharge ratio by sintering graphene and a metal oxide particle in air (U.S. Pat. No. 8,257,867), a method of manufacturing a graphene-TiO.sub.2 hybrid material by mixing a TiO.sub.2 nanopowder with graphene at a high temperature and high pressure and reacting them (US 2012-0149554 A), a method of manufacturing a graphene ceramic composite (KR 2012-0039799A, and KR 2013-0014327A), and the like have been explored.

In addition, Publication Laid-open KR 10-2012-0039799 discloses a technology of improving coating properties of graphene itself by directly chemically bonding a ceramic precursor with a carboxyl group (—COOH) on the edge of GO to improve dispersion. For example, the graphene itself is coated on the edge of the GO through a chemical bond and may induce high electrical conductivity. However, the coating may be weak, since there is no binder between the GO and the coated graphene layer. Publication Laid-open KR10-2013-0014327 also discloses a method of making a graphene composite by mixing a salt type (e.g., chloride) ceramic precursor with graphene or a graphene oxide and then, calcinating the mixture at a high temperature. However, when the ceramic and the graphene have a directly chemical bond, the sheet-shaped structure of the graphene itself is broken, and the graphene may lose inherent properties.

This problem becomes severe, particularly when the ceramic is oxide, since a carbon component in the graphene is bonded with an oxygen component in the ceramic and released as gas such as CO and CO.sub.2, leaving a carbon residue as a particle. When an oxide ceramic precursor or oxide ceramic sol is calcinated with graphene, there is a similar problem to the above.

In addition, when graphene is reacted at a low temperature that the graphene has no reaction with oxygen without calcination in order to reduce the problem, there is a stripping problem due to severe deterioration of an interface bond between oxide ceramic and graphene. In other words, hydrophobicity of the graphene may resist against hydrophilicity of the ceramic.

In general, when a ceramic film is formed by coating ceramic sol and gelating it, the film may be destroyed due to evaporation of a solvent and an osmotic pressure during the drying. Meanwhile, when graphene is used to form a hybrid film, the hybrid film including the graphene in an appropriate concentration is actually difficult to form due to diffusion of the graphene into a solvent and prevention of drying (non-uniform drying since a graphene layer is positioned on the surface and prevents movement and diffusion of the solvent).

The hybrid film has difficulty in terms of commercial availability, since the graphene is hardly dispersed layer by layer in a solid-phase matrix to realize properties of a graphene-containing composite. In addition, a specific process example has not been provided yet.

Accordingly, in order to solve the problems, a method of reducing a metal precursor at room temperature to powder it and platting and sputtering graphene to manufacture composite powder or a composite layer has been suggested, and another method of using a polymer resin in an entire amount to avoid the fundamental problem of a ceramic composite is mostly used.

However, the above graphene composite materials are not sufficiently dispersed, and the polymer resin also has a drawback of sharply deteriorating thermal conductivity of the graphene and durability of the film.

Summary of the invention

In preferred aspects, the present invention provides a graphene-containing coating film having improved thermal conductivity and surface functionality (hydrophilicity) and a method of preparing the same.

In one aspect, provided is a graphene-containing coating film. The coating film may comprise: at least one hydrate represented by Chemical Formula 1, graphene positioned on the surface, particularly in a shape of discontinuous island, of the hydrate represented by Chemical Formula 1, and a silica particle positioned on the surface of the hydrate of Chemical Formula 1 and positioned on the surface of the graphene in a shape of discontinuous island. In particular, the silica particle may include agglomeration of a plurality of silica nanoparticles. X.sub.n-M-(OH).sub.4-n [Chemical Formula 1]

In Chemical Formula 1,

M is selected from the group consisting of Si, Ti, Ag, Sn, In, and Zn, or a combination thereof,

X is: a) a C1 to C30 alkyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group; b) a C1 to C30 alkenyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group; or

c) a C1 to C30 alkynyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group, and

n is an interger of 1 to 3.

The “silica nanoparticles” as used herein refer to particles made of silica or substantially homogeneous silica and the particles may have average size less than about 990 nm, less than about 900 nm, less than about 800 nm, less than about 700 nm, less than about 600 nm, less than about 500 nm, or less than about 400 nm. The graphene-containing coating film may include: 1) a first region including the hydrate represented by Chemical Formula 1 and the silica particle bound with each other; and 2) a second region including the hydrate represented by Chemical Formula 1, the graphene and the silica particle bound with one another.

An average diameter of the silica particle of the first region may be from about 5 nm to about 50 nm, and an average diameter of the silica particle of the second region may be from about 5 nm to about 25 nm.

An average diameter of the silica nanoparticle may be from about 5 nm to about 30 nm. A thickness of the graphene may be from about 0.4 nm to about 5 nm. A major axis length of the graphene may be from about 100 nm to about 10,000 nm, and a minor axis length of the graphene may be from about 100 nm to about 900 nm.

An amount of the graphene may be from about 0.001 wt % to about 50 wt % based on the total weight of the hydrate represented by Chemical Formula 1, the graphene, and the silica nanoparticle.

When transmittance is greater than or equal to about 70%, the an amount of the graphene may be from about 0.001 wt % to about 3 wt % based on the total weight of the hydrate represented by Chemical Formula 1, the graphene, and the silica nanoparticle.

The “transmittance” as used herein refers to a fraction (%) of the light transmitted through the graphene-containing coating film film from the initially radiated light. The wavelength of the light transmitted the film is not particularly limited, but the transmittance may be measured with the light having the wavelength within infrared, visible light or ultraviolet (UV) light regions. For instance, the transmittance of the film may be measured at visible light regions at the wavelength of about 400 nm to 700 nm.

The graphene-containing coating film may have a thickness of about 100 nm to 2 μm.

When transmittance is greater than or equal to about 70%, the graphene-containing coating film may have a thickness of about 200 nm to 500 nm.

The Chemical Formula 1 may be represented by one of Chemical Formulae 1-1 to 1-3. X.sup.1-M-(OH).sub.3 [Chemical Formula 1-1] X.sup.1X.sup.2-M-(OH).sub.2 [Chemical Formula 1-2] X.sup.1X.sup.2X.sup.3-M-(OH) [Chemical Formula 1-3]

In Chemical Formulae 1-1 to 1-3,

M is selected from the group consisting of Si, Ti, Ag, Sn, In, and Zn, or a combination thereof,

X.sup.1, X.sup.2, and X.sup.3 are each independently a) a C1 to C30 alkyl group substituted or unsubstituted with at least one functional group selected from an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group;

b) a C1 to C30 alkenyl group substituted or unsubstituted with at least one functional group selected from an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group; or c) a C1 to C30 alkynyl group substituted or unsubstituted with at least one functional group selected from an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group.

Preferably, M may be Si or Ti.

The graphene-containing coating film may further include an additive selected from the group consisting of an inorganic powder, an organic additive, and a combination thereof.

The inorganic powder may have an average diameter of about 5 nm to 50 nm.

In another aspect, provided is a method of preparing a graphene-containing coating film. The method may comprise: dispersing a graphene; mixing and dispersing a silica nanoparticle and the precursor of the hydrate represented by Chemical Formula 1 in a hydrophilic solvent and mixing the same with the dispersed graphene; performing hydrolysis and condensation reactions of the mixed dispersed solution to prepare a graphene-containing sol solution; coating the graphene-containing sol solution on a substrate and drying the same at a temperature of about 25° C. to 400° C.; and heat-treating the dried film at a temperature of about 50° C. to 900° C.

The silica nanoparticle may be present in an amount of about 5 to 20 wt % based on the total amount of the mixed dispersed solution; the precursor of the hydrate represented by Chemical Formula 1 may be present in an amount of about 10 to 40 wt % based on the total amount of the mixed dispersed solution; the dispersed graphene may be present in an amount of about 0.001 to 15 wt % based on the total amount of the mixed dispersed solution; and the hydrophilic solvent may be present in a balance amount.

The graphene may dispersed by mechanical disperse treatment, or a solvent exchange method.

Preferably, the solvent exchange method may include: preparing dispersion by mixing a graphene powder, a first dispersing agent and a first non-aqueous based solvent; preparing a mixture by adding a second non-aqueous based solvent and a precursor of the hydrate to the dispersion; preparing a graphene-containing sol solution by mixing the mixture with a second dispersing agent and water.

In the process of the mixing and dispersing of a silica nanoparticle and the precursor of the hydrate represented by Chemical Formula 1 in a hydrophilic solvent and mixing the same with the dispersed graphene, an additive selected from the group consisting of an inorganic powder, an organic additive, and a combination thereof may be further included.

The inorganic powder may be mixed in an amount of about 5 parts by weight to 30 parts by weight based on 100 parts by weight of the mixed dispersed solution.

The organic additive may be mixed in an amount of about 0.01 parts by weight to 10 parts by weight based on 100 parts by weight of the mixed dispersed solution.

Preferred precursors of the hydrate represented by Chemical Formula 1 may be , for example, selected from the group consisting of trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, isobutyltriethoxysilane, glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane allyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N,N-dimethylaminopropyl)triethoxysilane, and N,N-{(2-aminoethyl) (3-aminopropyl)}trimethoxysilane, or a combination thereof.

Further provided are vehicle parts that comprising the graphene-containing coating film as described above. Such vehicle parts may include a head lamp of a vehicle.

The present invention also includes vehicles that comprise a vehicle part such as a head lamp that comprises the graphene-containing coating film as described herein.

The present invention may provide a graphene-containing sol solution having improved stability and dispersability. In particular, the graphene-containing coating film may have improved dispersion of graphene, an interface bond, graphene stability, and surface functionality. Further provided are vehicle parts such as a head lamp of a vehicle comprising the graphene-containing coating film as described herein.

Also provide are vehicles that comprise the vehicle parts such as a head lamp that comprises the graphene-containing coating film as described herein.

Brief description of the drawings

FIG. 1 shows a FE-SEM photograph of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIGS. 2A-2B show exemplary graphene-containing coating films according to Example 1 ( FIG. 2C ), and Comparative Examples 1 ( FIG. 2A ) and 2 ( FIG. 2B ).

FIG. 3 shows various forms of hydrate included in an exemplary coating composition for forming an exemplary graphene-containing sol according to an exemplary embodiment of the present invention.

FIG. 4 shows the condensed form of an exemplary hydrate precursor in an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIG. 5 is a graph showing the content of graphene in graphene-containing coating films maintaining sol stability in various exemplary embodiments of the present invention.

FIG. 6 shows a photographic view of dispersion stability and storage-stability of an exemplary coating composition for forming an exemplary graphene-containing sol according to an exemplary embodiment of the present invention.

FIG. 7 shows a photographic view of uniformity and transparency of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIG. 8 is a graph showing transmittance of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIG. 9 is a graph showing thermal conductivity of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIG. 10 shows waterdrop contact angle of exemplary graphene-containing coating films according to various exemplary embodiments of the present invention.

FIG. 11 shows a field emission-scanning electron microscope (FE-SEM) photograph of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

FIG. 12 shows FE-SEM photographs of exemplary heat-treated graphene-containing coating films according to various exemplary embodiments of Comparative Example and the present invention.

Description of symbols

10 : ceramic sol

20 : graphene

30 : silica nanoparticle DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

Further, it is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

Hereinafter, embodiments of the present invention are described in detail. However, these embodiments are exemplary, and this disclosure is not limited thereto.

An graphene-containing coating film according to an exemplary embodiment may comprise: at least one hydrate represented by Chemical Formula 1, a graphene positioned in a shape of discontinuous island on the surface of the hydrate represented by Chemical Formula 1 and a silica particle positioned on the surface of the hydrate of Chemical Formula 1 and positioned on the surface of the graphene in a shape of discontinuous island. In particular, the silica particle may include agglomeration of a plurality of silica nanoparticles. X.sub.n-M-(OH).sub.4-n [Chemical Formula 1]

In Chemical Formula 1,

M is selected from the group consisting of Si, Ti, Ag, Sn, In, and Zn, and a combination thereof,

X is: a) a C1 to C30 alkyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group; b) a C1 to C30 alkenyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group; or c) a C1 to C30 alkynyl group substituted or unsubstituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group, and a substituted or unsubstituted C1 to C10 silyl group.

n is an integer of 1 to 3.

The hydrate represented by Chemical Formula 1 may be stably bound to the interface of the silica nanoparticle and the graphene in a hydrophilic sol solution because an organic functional group of the hydrate is fused with a hydrophilic group of the hydrophilic sol solution due to at least one organic functional group represented by “X”. These may be stable during drying and heat-treating processes, and have buffering effect even an excess amount of an organic additive and an organic additive, forming a stable film.

The functional group of the hydrate may have hydorphilic characteristics, for example an epoxy group, a ketone group, a carboxyl group, a hydroxy group, an amino group, an amine group (e.g., primary, secondary, or tertiary amine), a thiol group, a phosphoric acid group, a halide group (e.g., F, Cl, Br, or I), an ester group, or an alkyl group, an alkenyl group, or an alkynyl group including O, S, P, N, Si, and the like in the backbone, or a salt of an organic or inorganic material.

X is not particularly limited to a size of a molecular weight. However, when being an oligomer, a macromolecule or a polymer, X may bind neighboring molecules by a hydrated functional group therein being capable of inducing a second, a third sol-gel reaction, that is —Si—OH, —Si(OH).sub.2, or —Si(OH).sub.3 and may spread a sol-gel reaction.

Examples of the organic functional group of X may be a substituted or unsubstituted C1 to C30 alkyl group; C1 to C30 alkenyl group; or C1 to C30 alkynyl group substituted with at least one functional group selected from the group consisting of an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group and a substituted or unsubstituted C1 to C10 silyl group.

By stating herein that a particular group may be “substituted or unsubstituted” means that the group may be optionally substituted at one or more available positions by groups such as, for example, an epoxy group, a glycidoxy group, a vinyl group, an acryl group, a methacryl group, a carboxyl group, an amino group, a thiol group, a phosphoric acid group, a fluoro group, a chloro group, a bromo group, an iodine group, a hydroxy group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C1 to C10 ketone group, a substituted or unsubstituted C1 to C10 amine group, a substituted or unsubstituted C1 to C10 sulfur group, a substituted or unsubstituted C1 to C10 ester group and a substituted or unsubstituted C1 to C10 silyl group.

The Chemical Formula 1 may be represented by one of Chemical Formulae 1-1 to 1-3. X.sup.1-M-(OH).sub.3 [Chemical Formula 1-1] X.sup.1X.sup.2-M-(OH).sub.2 [Chemical Formula 1-2] X.sup.1X.sup.2X.sup.3-M-(OH) [Chemical Formula 1-3]

In Chemical Formulae 1-1 to 1-3, X.sup.1, X.sup.2 and X.sup.3 may be the same as X, or may be different.

M may be selected from the group consisting of Si, Ti, Ag, Sn, In, and Zn, and a combination thereof. Preferably, M may be Si or Ti.

In an exemplary embodiment, when the M is Si, exemplary precursors of silicon-based compounds may be selected from the group consisting of trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, prop yltrimethoxysilane, prop yltriethoxysilane, isobutyltriethoxysilane, glycidoxypropyltriethoxysilane, cyclohexyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane allyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane and diphenyldiethoxysilane, (N,N-dimethylaminopropyl)trimethoxysilane, (N,N-dimethylaminopropyl)triethoxysilane, and N,(2-aminoethyl)(3-aminopropyl)trimethoxysilane, or combinations thereof, but are not limited thereto.

In addition, the silicon-based compounds may be precursors that have a M-OR bond (alkoxy bond) with other metal, M, or a M-OOR bond (ester bond).

Preferably, the hydrate represented by Chemical Formula 1 may be a hydrolyzed ceramic precursor, for example X.sup.1-Si—(OH).sub.3, X.sup.1X.sup.2-Si—(OH).sub.2, X.sup.1X.sup.2X.sup.3-Si—(OH) and the like as shown in FIG. 3 . Herein, when an organic material component, a precursor reagent including X.sup.1, X.sup.2, and X.sup.3 is hydrolyzed, modified groups (chemical modificatin, or formation of a complex, or a salt) of X.sup.1, X.sup.2 and X.sup.3, interface properties with graphene may be improved and organic materials may first react with carbon of the graphene, protecting graphene.

The X.sup.1, X.sup.2, and X.sup.3 may be the same or different.

During formation of the graphene-containing coating film, X.sup.1, X.sup.2, and X.sup.3 may be polymerized (forming a network) as shown in FIG. 4 . It may have a condensed form where a —Si—O—Si-bond is formed, and substituent moieties of X.sup.1, X.sup.2, and X.sup.3 may provide a —Si- and —O—Si-bond. Particularly, when a X moiety includes an organic functional group such as an epoxy group, a hardener may be used to cure the X moiety.

The hardener may cure a curable resin, and the curing may be performed by a reaction using a catalyst, or cross-linking by a hardener.

The hardener is not particularly limited, and may be any commercial compound for a hardener of a general epoxy resin. For example, the hardener may be selected from the group consisting of an amine-based compound, an amide-based compound, an acid anhydride-based compound, a phenol-based compound and the like. Specifically, the amine-based compound may be diaminodiphenylmethane, ethylenediamine, diethylenetriamine, triethylenetetramine, diaminodiphenylsulfone, isophoronediamine, imidazole, BF3-amine a complex, guanidine derivative, and the like, the amide-based compound may be dicyandiamide, a polyamide resin synthesized from a linolenic acid dimer ethylenediamine, an acid anhydride-based compound, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and the like, the phenol-based compound may be a polyvalent phenol compound such as a phenolnovolac resin, a cresolnovolac resin, an aromatic hydrocarbon formaldehyde resin a modified phenol resin, a dicyclopentadienephenol addition-type resin, a phenolararkyl resin (xylok resin), a polyvalent phenolnovolac resin synthesized from a polyvalent hydroxy compound and formaldehyde such as resorcin novolac resin, a naphtholararkyl resin, a trimethylolmethane resin, a tetraphenylolethane resin, a naphtholnovolac resin, a naphthol-phenol cocondensed novolac resin, a naphthol-cresol cocondensed novolac resin, a biphenyl modified phenol resin (a polyvalent phenol compound including a bismethylene group linked to a phenolic nucleus), a biphenyl modified naphthol resin (a polyvalent naphthol compound including a bismethylene group linked to a naphtholic nucleus), a aminotriazine modified phenol resin (a polyvalent phenol compound including melamine, benzoguanamine, and the like linked to phenolic nucleus by a methylene bond) or an alkoxy group-containing aromatic ring modified novolac resin (a polyvalent phenol compound including a phenolic nucleus and alkoxy group-containing aromatic ring linked to formaldehyde) and mixtures thereof.

In an epoxy resin composition of the present invention, amounts of an epoxy resin and a hardener are not particularly limited, but active groups of the hardener may be preferably used in about 0.7 to 1.5 equivalents based on 1 equivalent of the sum of epoxy groups of an epoxy resin.

For example, in the case of glycidoxypropyltriethoxysilane, a hardener such as ethylene diamine may be used for an epoxy group that is an organic functional group of X moieties.

The graphene may be positioned in a shape of discontinuous island on the surface of the hydrate represented by Chemical Formula 1, and a silica particle including a plurality of silica nanoparticle may be agglomerated and positioned on the surface of the graphene.

The “shape of discontinuous island” means that a plurality of island shapes are discontinuously arranged, and the island shape refers to a spherical, semispherical, non-spherical, or amorphous shape having a volume, but it is not limited to these specific shapes.

The graphene may improve thermal conductivity, and may be positioned in a shape of discontinuous island, that is a thin and wide sheet-shape on the surface of the hydrate represented by Chemical Formula 1, and thus stability may increase at the interface between the hydrate represented by Chemical Formula 1 and graphene and at the interface between the graphene and the silica nanoparticle.

Particularly, since the silica particles on the surface of the graphene has relatively dense agglomeration relative to silica particle on the surface of the hydrate represented by Chemical Formula 1, a small amount of grain boundaries between the particles may be distributed, and thus it may have a favorable structure for providing characteristics near to hyperhydorphilicity and improved thermal conductivity characteristics.

A thickness of the graphene may be from about 0.4 nm to 5 nm, from about 0.4 nm to about 4 nm, or particularly from about 0.4 nm to about 2.8 nm.

The graphene may have a thickness of about 4 nm, when it has about 10 layers at maximum and a thickness of about 2.8 nm, when it has about 7 layers at maximum.

A major axis length of the graphene may be from about 100 nm to about 10,000 nm, and a minor axis length of the graphene may be from about 100 nm to about 900 nm.

Particularly, the major axis length may be from about 100 nm to about 2,000 nm, and the minor axis length may be from about 100 nm to about 500 nm.

When the graphene has the above thickness and size, hydrophilicity and thermal conductivity of the graphene-containing coating film may be improved, and further hyperhydrophilicity may be provided.

Prefereably, the graphene of the present invention may be a sheet-shaped material having a BASAL plane with a thickness of an atom/molecule to a nano unit, for example, graphene oxide (graphite oxide) consisting of sheet-shaped BASAL planes comprising carbon, rGO (reduced graphene oxide), and a graphene nanoplate (stripped expanded graphite) and further, modified graphene oxide (modification of a substituent, a derivative, a combination with a third material, and like) or doped graphene oxide.

The graphene of the present invention may be manufactured by preparing graphene oxide (commonly called to be GO), radiating energy into the graphene oxide (using a microwave, a photon, IR, a laser, and the like) or reducing the GO in a liquid phase, a gas phase, and a solid-phase. Herein, the reduction includes thermal reduction and chemical reduction.

In addition, the graphene may be stripped layer by layer after being dipped in a solvent having excellent affinity with with graphite and then, treated by an ultrasonic wave and the like. The solvent having excellent affinity with graphite may representatively include GBL, NMP, and the like. The graphene obtained in this method can have good quality but difficulty in a mass production.

In addition, the graphene may be obtained from a chemical synthesis method, a bottom production method, a method of chemically spliting carbon nanotube and folding it, and the like. Further, the graphene may be obtained from a solvent-stripping method of graphite, a mechanically-grinding method of graphite (ultrasonic wave, milling, a gas-phase high speed blading method, an electrical stripping method, a synthesis method, and the like.

On the other hand, oxidizing groups on the surface of the graphene may be completely removed by any currently-known method, and an oxygen content by the oxidizing groups on the surface of the graphene except for GO may be less than or equal to about 5 wt % based on the amount of a carbon backbone. In the present invention, unless otherwise indicated, ‘graphene’ is defined when the oxygen content by oxidizing groups on the surface is even less than or equal to about 5 wt % based on the amount of a carbon backbone.

In the present invention, all the above forms are uniformly called as graphene.

In the present invention, highly dispersed graphene is used, and a method of dispersing graphene is described in connection with a manufacturing method later.

The graphene-containing coating film may include 1) a first region including the hydrate represented by Chemical Formula 1 and the silica particle bound with each other; and 2) a second region including the hydrate represented by Chemical Formula 1, the graphene and the silica particle bound with one another.

A structure of the graphene-containing coating film according to an exemplary embodiment of the present invention can be described referring to FIG. 1 .

FIG. 1 shows a FE-SEM photograph of an exemplary graphene-containing coating film according to an exemplary embodiment of the present invention.

Referring to FIG. 1 , an A region corresponds to the second region, and a B region corresponds to the first region.

The first and second regions may be distinguished by a silica particle shape on the mostouter surface.

The silica particle may comprise silica nanoparticles mostly having an average diameter ranging from about 5 nm to about 30 nm, the silica nanoparticles may be agglomerated and variously shape the silica particle. The shape of the particle may be determined depending on a region where these silica nanoparticles are present, that is, a region where these silica nanoparticles are present on the surface of hydrate or where these silica nanoparticles are present on the surface of graphene. The silica nanoparticle may have an average particle diameter ranging from about 5 nm to about 30 nm, or particularly, from about 7 nm to about 25 nm, and accordingly, the present invention may use a silica nanoparticle having, for example, an average particle diameter of about 7 nm, about 15 nm, or about 25 nm.

The description continues in the full USPTO document.